The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Integrated circuits typically use materials with low dielectric constants (low-k) as an intermetal and/or interlayer dielectric for conductive interconnects. Use of low-k materials tends to reduce the delay in signal propagation due to capacitive effects. As the dielectric constant decreases, the capacitance of the dielectric and the RC delay of the integrated circuit (IC) also tend to decrease.
Low k dielectrics typically refer to materials having a dielectric constant lower than silicon dioxide (k<=4). Typical methods for providing low-k materials include doping silicon dioxide with a hydrocarbon or fluorine. The doping methods, however, generally do not produce materials with dielectric constants lower than about 2.6. Ultra low-k (ULK) dielectric materials can be obtained by incorporating air voids within a low-k dielectric, which creates a porous dielectric material.
Methods of fabricating porous dielectrics typically involve forming a composite film with a porogen and a dielectric material. Once the composite film is formed on the substrate, the porogen component is removed, which leaves a porous dielectric matrix. Techniques for removing porogens include heating the substrate to a temperature sufficient to break down and vaporize the porogen. However, substrate temperatures generally need to be high over a long exposure period, which can damage copper containing substrates.
A porous low-k or ULK film of dielectric material can also be formed using a precursor film that contains a porogen and a structure former on a substrate. The precursor film is then exposed to ultraviolet (UV) radiation to remove the porogen. This approach tends to form porogen deposits on a window through which the UV light is transmitted. The porogen deposits inhibit UV light transmission. As a result, only a few substrates can be cured before cleaning is required. Purge rings with gas delivery baffles may be used to prevent the accumulation of ultralow-dielectric (ULK) byproducts on windows and other surfaces within a UV thermal processing (UVTP) system.
Referring now to FIG. 1, a purge ring 102 includes an inlet portion 104 and an exhaust portion 106. The inlet portion 104 comprises a side wall 108 having an inner surface 109. The exhaust portion 106 comprises a side wall 110 having an inner surface 111. The purge ring 102 provides purge gas to an inner region 112 via an inner surface 109 of the inlet portion 104 and exhausts the purge gas from the inner region 112 via the inner surface 111 of the exhaust portion 106.
The purge ring 102 further includes a plenum 120 indicated by dashed lines in FIG. 1 and a baffle 122. During periodic cleaning operations, cleaning gas flows through the plenum 120 and the baffle 122 into the inner region 112 to clean a window surface and other portions of the photonic temperature processing system.
The purge ring 102 includes a gas inlet 126 located in the inlet portion 104 at end 127. The purge ring 102 further comprises an exhaust channel 130 located in the exhaust portion 106 (indicated by dotted lines in FIG. 1). The purge ring 102 includes an exhaust opening 132 on the inner surface 111 of the exhaust portion 106. Gas and other matter (e.g., suspended particulate matter) flows from the inner region 112 into the exhaust channel 130. Gas and other matter flows into an exhaust outlet 136, which is located at end 137. Typically, an exhaust pump (not shown) provides suction to draw the gas and other matter from the inner region 112 through the exhaust channel 130 and the exhaust outlet 136. Flow arrows 140 represent the flow of the gas from the plenum 120 through the baffle 122 into the inner region 112. Flow arrows 150 represent the flow of the gas out of the inner region 112 into the exhaust channel 130.
Referring now to FIG. 2, a cross-sectional view 200 of the side wall 108 of the inlet portion 104 is presented. The side wall 108 includes a lower portion 202 and an upper portion 204 defining the plenum 120 and the baffle 122. Gas flows through the baffle 122 to the inner region 112.
Referring now to FIG. 3, an example photonic temperature processing system 300 is shown to include the purge ring 102. The photonic temperature processing system 300 includes a chamber 306 with a pedestal 308, which holds a substrate 310 such as a semiconductor wafer. A pedestal heater 312 may be used to heat the substrate 310 and other components, such as the purge ring 102. The photonic temperature processing system 300 further comprises one or more UV lamps 316 for providing UV light and heat for curing the substrate 310 located. The purge ring 102 may be located between a window 318 and the pedestal 308. The UV lamps 316 and the window 318 may be located in a lamp assembly 320.
The photonic temperature processing system 300 includes a inlet conduit 340 coupled to the gas inlet 126. An exhaust conduit 342 is coupled to the exhaust outlet 136. The photonic temperature processing system 300 further comprises a top plate 330 that is configured to support and spatially to orient the purge ring 102 and the lamp assembly 320, including the window 318.
The inlet conduit 340 and the exhaust conduit 342 may be integral with the top plate 330. Typically, the photonic temperature processing system 300 is connected to one or more gas sources 360 that provide gas through the inlet conduit 340 to the purge ring 102. The gas sources 360 may include a purge gas such as argon 362, nitrogen 364, oxygen 366, and a cleaning gas 368 such as a remote plasma cleaning (RPC) unit for providing radical oxygen gas O′ to the photonic temperature processing system 300. The purge gas may be preheated by a heater 369.
During purging or cleaning, gas flows from the gas sources 360 through the inlet conduit 340 into the plenum 120, as indicated by gas flow arrow 370. The gas then passes from the plenum 120 through the baffle 122 into the inner region 112 of the purge ring 102. The gas flows through the inner region 112 as indicated by gas flow arrow 372. From the inner region 112, the gas and other matter enters the exhaust channel 130, as indicated by flow arrow 374. The gas and other matter exits the photonic temperature processing system 300 through the exhaust conduit 342. An exhaust pump 376 draws the gas and other matter from the inner region 112 through the exhaust channel 130, the exhaust outlet 136 and the exhaust conduit 342.
Although the purge ring 102 is relatively efficient at keeping the window 318 clean, it cannot prevent all porogen accumulation on the window 318. As a result, cleaning is required after processing a batch of wafers to restore UV transmission intensity through the window 318. The porogen material also may adhere to other areas of the chamber 306 and may eventually cause particles to be formed.
The most efficient known method of cleaning the window 318 is to flow cleaning gas such as remotely generated O-plasma (RPC) through the baffle 122. In the purge ring 102, the cleaning gas species flows through a restriction (the baffle 122). The restriction compresses the O-plasma and causes it to recombine into oxygen. This recombination reduces the available clean species, which restricts the effectiveness of the cleaning gas.
In order to clean the rest of the chamber 306, a second clean step is usually performed. The second clean step involves using the UV lamp 316 to create ozone throughout the chamber 306. While this approach is effective in cleaning the chamber 306, it is a lengthy process that adds a significant amount of time to each clean. Current cleaning procedures require about 5 minutes of RPC and 20 minutes of ozone, with additional overhead required to pressurize the chamber 306 between the RPC and ozone cleaning. This long clean procedure cuts system throughput, requires a large amount of gas, and does not always sufficiently clean the chamber 306 and the window 318.